Howie,
Try leaving your pump on the water heater on for a couple days, see if you make temp in the room, 5 minutes on, then off, then on???
You should control the pump with a line volt T stat. Assuming the building can get warm, then the pump would shut off,
Curious what is the BTU load rating on the wood fired unit, sounds a bit large.
Happy New Year all,
Dan

to OP,

First, stop turning off the pump. it is adding BTUs whether the temperature rises or not, all you are doing turning it off is reducing the amount of energy it puts into the water. Dan I think was trying to say that same thing. it's not about water temp it's about BTUs, you don't have water temp because you don't have the BTUs... you can't cheat by turning the pump off.

Second, it is very unlikely to be sized appropriately. It might provide freeze protection for the garage at least, but that's about it. A real heat load calculation should be done. Then an appropriately sized heat source should be put in. There is no other path forward. the good news is electric boilers are not that expensive, typically.

Correct Rob,
Howie had mentioned he was turning the pump on and then off in short runs, that is pointless and will defeat the potential of what BTU may be available,
I agree with Rob, the best you may expect is freeze protection and a slight warmer space.
Dan

Very interesting. Just doing something similar with 480 sq ft. in Vancouver. 2" foam under, r20 walls, insulated steel doors front and back,r40 ceiling. Pro heat loss calcs and followed install specs. It was all great until the supplier, who is not a radiant pro, tells me the only tank I can use is $2100 and has side tappings.Was planning a 40 gal gas fired HW tank. I don,t understand the requirement and have seen other installs with standard type hot water tanks. Can anybody shed some light on this?
Thanks in advance..

Very interesting. Just doing something similar with 480 sq ft. in Vancouver. 2" foam under, r20 walls, insulated steel doors front and back,r40 ceiling. Pro heat loss calcs and followed install specs. It was all great until the supplier, who is not a radiant pro, tells me the only tank I can use is $2100 and has side tappings.Was planning a 40 gal gas fired HW tank. I don,t understand the requirement and have seen other installs with standard type hot water tanks. Can anybody shed some light on this?
Thanks in advance..

Howdy boys ... I myself have tried this too a 28 x 48 garage @ 13ft high ceilings and an apartment above 12/12 pictch ... we feel the cold from the floor below since I didn't insulat the ceiling ... I put 1" or polyclosed cell under the slab plus 2' around the perimitor r23 in the walls and insulated doors 2 10 x 10 doors.

Well after a few attemps I came across this and am going to give it a try "wish me luck" I'm going to put in a 80gallon HW Tank and heat it with a Geyser heat pump ... with 1200 feet of 1/2 pex 4 zones I'm hoping this does the job ... also I do have the desuperheater in the geo furnace unfortunatly the installer didn't belive in hydronic heat or we would have gone water to water over water to air! Check it out if you will ... I will post back my results ... Nyle.com ... most people that have used this for their domestic hot water heat have said that with a family of 3 and an 80-gallon tank it never used any electricity the pump kept up with their use?